S.F.
I think this is a phase. When children are around 3 years old, then do not have the reasoning skills to easily differentiate between appropriate behavior. My sons have both gone through this.
I have to watch them closely when playing with other kids, girls or younger children. They do not realize that other kids do not know their games. I try to teach them to use their words and ask the kids if they want to play tag, Duck Duck Goose or whatever. Then I tell them they need to use "gentle touches". I practice "gentle touches" with the kids when petting small animals. Whenever we see a neighbor dog, I ask the owner if we can pet the animal. I tell and show the kids how to do "gentle touches". I hold their hands and help them stroke the animal softly. Then I use the same wording when they are playing with friends. They have created a mental image when petting the animal. They are able to remember the experience because they enjoy the attention and action. I tell them that because they are gentle with the animal that they are able to play with the animal and pet them. I tell them it is the same thing with other children. If we are gentle, polite and compassionate, others will want to be around us and play with us.
I tell watch my kids like a hawk when they are with others. But... I really think that the visual image and practice of petting animals, focusing on the message and then re-interating that message with friends helps. I try to teach the kids to touch a person and not push. Pushing and hitting is never okay... even when playing. It's hard for adults to understand this sometimes, especially men...lol, but I think it's important to emphasize because young children do not know their own strength or how to control it.